TiO₂ core-shell and core-dual-shell nanoparticles with tunable heterojunctions and visible to near-infrared extinctions

The popular use of titanium dioxide (TiO₂) among metal oxides in a variety of optoelectronic applications can be attributed to its low cost and strong extinction in the UV region. However, TiO₂ suffers from an inability to utilize a major part of the solar spectrum, and from rapid electron-hole recombination of photo-generated charge carriers. These challenges can be resolved by incorporating gold-silver nanoshells (GS-NS) with localized surface plasmon resonances (LSPR) into TiO₂ nanostructures, with the overall goal of understanding near-field LSPR activation as well as electron-transfer and charge-trapping characteristics in core-shell and core-dual-shell systems. A method for the synthesis of core-shell nanoparticles consisting of a hollow gold-silver nanoshell core with a TiO₂ shell (GS-NS@TiO₂) is presented. Synthesis of core-dual-shell nanoparticles with either a semiconducting or insulating interlayer between the GS-NS core and TiO₂ shell (GS-NS@SnO₂@TiO₂ and GS-NS@SiO₂@ TiO₂) is also presented. In addition to a strong tunable surface plasmon resonance in the visible to near-IR region that allows better utilization of the solar spectrum by the TiO₂ shell, incorporation of a GS-NS core leads to significant suppression of electron-hole recombination processes in TiO₂, further demonstrating the advantages of the plasmonic core and metal oxide shell architecture. The near-field LSPR properties and charge transfer characteristics were further modified by the incorporation of SnO₂ or SiO₂ interlayers, with the SnO₂ interlayer providing the most effective suppression of charge recombination. Reliable methods to fabricate composite TiO₂-based nanoparticles with finely tunable optical and electrical properties are reported.